The present invention relates to a liquid crystal display module and a liquid crystal display monitor mounting the liquid crystal display module.
The liquid crystal display devices have been widely used as a display device capable of displaying high-definition color images for a notebook personal computer and a display monitor. The liquid crystal display device comprises a liquid crystal display panel having a liquid crystal layer sandwiched between a pair of transparent substrates, an illuminating device for visualizing latent images electronically formed in the liquid crystal display panel, and an optically compensating sheet disposed between the liquid crystal display panel and the illuminating device. These components can be assembled as an integral unit which is capable of being mounted into a notebook personal computer or a liquid crystal display monitor, and which is commonly called a liquid crystal display module.
Among the well-known liquid crystal display devices, one type is a simple-matrix type liquid crystal display device incorporating a simple-matrix type liquid crystal display panel having a liquid crystal layer sandwiched between a pair of substrates each formed with parallel strip electrodes on their inner surfaces arranged such that the parallel strip electrodes on one of the pair of substrates intersect those on the other of the pair of substrates, and another type is an active-matrix type liquid crystal display device incorporating a liquid crystal display panel provided with switching elements on one of a pair of substrates sandwiching a liquid crystal layer such that each of the switching elements selects a corresponding one of pixels of the liquid crystal display panel.
The active-matrix type liquid crystal display panel is divided into a so-called vertical electric field type (commonly called the TN type) which is represented by the TN (Twisted Nematic) type and uses a liquid crystal display panel having plural strip electrodes formed on each of a pair of upper and lower substrates for selecting pixels, and a so-called horizontal electric field type (commonly called IPS (In-Plane Switching) type) which uses a liquid crystal display panel having plural electrodes formed only on one of a pair of upper and lower substrates for selecting pixels.
In the TN type liquid crystal display panel, the liquid crystal molecules are aligned to twist by 90 degrees, for example, between a pair of upper and lower substrates, a pair of polarizers are disposed on the outer surfaces of the upper and lower substrates of the liquid crystal display panel, respectively, with their absorption axes oriented in the cross-Nicole arrangement, and the absorption axis of the entrance-side polarizer is aligned in parallel with or perpendicularly to a rubbing direction of the entrance-side substrate.
In the TN-type active-matrix type liquid crystal display panel, when a voltage is not applied across the liquid crystal layer, the linearly polarized light entering the liquid crystal layer through the entrance-side polarizer propagates along the twist of the liquid crystal molecules of the liquid crystal layer, if the transmission axis of the exit-side polarizer is coincident with the azimuthal angle of the plane of polarization of the linearly polarized light leaving the liquid crystal layer, all the linearly polarized light exits from the liquid crystal display panel to produce a white display (the so-called normally open mode), but, on the other hand, when a voltage is across the liquid crystal layer, a director which is a unit vector representing a direction of the average alignment of the axes of the liquid crystal molecules of the liquid crystal layer is perpendicular to the major surface of the substrate, therefore the azimuthal angle of the plane of polarization of the linearly polarized light entering the liquid crystal layer is not changed, and consequently, the azimuthal angle of the plane of polarization of the linearly polarized light leaving the liquid crystal layer becomes coincident with that of the absorption axis of the exit-side polarizer, and produces a black display (For further detail, see “Basics and Application of Liquid Crystal,” Industrial Research Association, Tokyo, 1991.).
On the other hand, in the IPS type liquid crystal display panel which has plural electrodes and wiring therefor for selecting pixels formed only on one of a pair of substrates, switches the liquid crystal molecules in planes parallel with the major surface of the substrates by applying a voltage between adjacent electrodes (a pixel electrode and a counter electrode) on the substrate, the polarization axes of the polarizers are arranged so as to produce a black display when no voltage is applied between the adjacent electrodes (the so-called normally closed mode).
In the IPS type liquid crystal display panel, the liquid crystal molecules in an initial state are in a homogeneous orientation in which the axes of the liquid crystal molecules are parallel with the major surfaces of the substrates, and the director of the liquid crystal molecules are parallel with or inclined at a small angle with a direction of the electrode wiring in planes parallel with the major surfaces of the substrates when no voltage is applied between the adjacent electrodes, and if a voltage is applied between the adjacent electrodes, the director of the liquid crystal molecules rotates toward a direction perpendicular to the direction of the electrode wiring according to the applied voltage. When the director is inclined at 45 degrees with respect to a direction of the director where no voltage is applied between the adjacent electrodes, the liquid crystal layer having a voltage thereacross serves to rotate the the azimuthal angle of plane of polarization through 90 degrees like a half-wave plate such that the azimuthal angle of plane of polarization of the light becomes coincident with the transmission axis of the exit-side polarizer, resulting in production of a white display.
The IPS type liquid crystal display panel has advantages that hue and contrast of a display vary little with viewing angles and consequently, their viewing angles are increased (See Japanese Patent Application National Publication No. Hei 5-505, 247 published on Aug. 5, 1993 which corresponds to WO91/10936 of PCT).
The most commonly used system for producing a full color display in the liquid crystal display devices using the above-explained types of liquid crystal display panels is one using color filters. In this system, one pixel corresponding to one dot capable of producing a color display is subdivided into three subpixels provided with three color filters corresponding to three primary colors, red (R), green (G) and blue (B), for example, respectively.
Recently, the liquid crystal display devices have been increased in screen size and in display resolution, and hence the liquid crystal display modules incorporated into the liquid crystal display device have been increased in weight. As for an external shape of the liquid crystal display modules, there has been a strong demand for reduction of a border area around a useful display area of a notebook personal computer or a liquid crystal display monitor incorporating such liquid crystal display modules. This is attributable to a demand that the outside dimensions of the notebook personal computer or the liquid crystal display monitor be made as small as possible. Hereinafter, the notebook personal computer and the liquid crystal display monitor may be referred to as the liquid crystal display monitor and the like.
The small outside dimensions can mean a superior saving in space, and as for design, the screen area of the liquid crystal display monitor appears larger if its border area around its useful display area is made smaller.